Micropolarity of Reverse Micelles of Aerosol-OT in n-Hexane

Correa, N. Mariano; Biasutti, M. Alicia; Silber, Juana J.

doi:10.1006/jcis.1995.1226

Cited by 137 publications

(261 citation statements)

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“…So far, a number of spectroscopic studies have been reported on reverse AOT micelles. [7][8][9][10][11][12][13][14][15][16][17][18][19][20][21] However, detailed discussion based on k nr has been rarely explored. The present study showed clearly that detailed analysis of the photophysical parameters was essential to discuss fluorescence characteristics of a probe molecule in reverse micelle systems.…”

Section: Energy Gap Dependence Of the Non-radiative Rate Constant Of Ansmentioning

confidence: 99%

“…As one of the several advantages of a reverse AOT micellar system, the size of the water pool can be controlled precisely at the nanometer level through the molar ratio of water to AOT: 7 Therefore, size effects on chemical and physical properties in nanometer dimensions can be studied by the use of reverse AOT micelles. Indeed, reverse AOT micelles have been studied by various techniques such as fluorescence spectroscopy [7][8][9][10][11][12][13][14][15][16][17][18][19][20][21] , NMR 22,23 , ESR 24,25 , IR [26][27][28] , and so on. [29][30][31][32] These studies demonstrated that polarity [8][9][10] , viscosity 11 , pH 12 , and other properties 30,32 of the water pool in the micelles were different from those in the bulk state and were dependent on the w 0 value.…”

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confidence: 99%

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Energy Gap Dependence of the Nonradiative Decay Rate Constant of 1-Anilino-8-naphthalene Sulfonate in Reverse Micelles

et al. 1999

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Spectroscopic or electrochemical analysis of a solute(s) confined in a minute volume is one of the promising approaches toward ultratrace analyses. Recent advances in various microspectroscopies and highly sensitive detection techniques have provided such new analytical methods. Furthermore, these techniques have revealed characteristics of chemical and physical phenomena in minute dimensions. As an example, our group reported previously that the rates of electron transfer and mass transfer across single microdroplet/water interfaces depended on the size of the droplet, as demonstrated by a laser trapping-spectroscopy-electrochemistry method. 1-4 Molecular association of a dye in individual micrometer-sized water droplets was also shown to be facilitated by decreasing the droplet size. 5,6 These size effects are observed owing to an increase in the surface area/volume (A/V) ratio of a droplet as the size decreases. Actually, the droplet size effects mentioned above (droplet diameter (d )>10 µm) were explained in terms of a change in the A/V ratio of the droplet. 2 For droplets with d<10 µm, on the other hand, other characteristic droplet size effects, caused by a change in droplet/solution interfacial structures or by thermal fluctuations of the interface, have been observed. 3,4 Clearly, the roles of a surface or interface in determining chemical and physical characteristics of a droplet become important as the size decreases. In submicrometer -nanometer dimensions, therefore, more pronounced size effects are expected. At the present stage of our investigation, however, a droplet size studied by the laser trappingspectroscopy-electrochemistry technique is limited to d>2 µm. In order to obtain knowledge which would bridge characteristic behavior in micrometer and in nanometer dimensions, experimental approaches other than the laser trapping method are necessary.As a system comprised of nanometer-sized droplets, reverse micellar systems have attracted broad interests, these are the systems in which water droplets (or water pools) are surrounded by surfactant molecules and an oil phase. 7 In particular, reverse AOT (sodium bis(2-ethylhexyl)sulfosuccinate) micelles have been studied extensively during the past decades.7-32 As one of the several advantages of a reverse AOT micellar system, the size of the water pool can be controlled precisely at the nanometer level through the molar ratio of water to AOT: w 0 =[H 2 O]/[AOT]. 7 Therefore, size effects on chemical and physical properties in nanometer dimensions can be studied by the use of reverse AOT micelles. Indeed, reverse AOT micelles have been studied by various techniques such as fluorescence spectroscopy 7-21 , NMR 22,23 , ESR 24,25 , , and so on. [29][30][31][32] These studies demonstrated that polarity 8-10 , viscosity 11 , pH 12 , and other properties 30,32 of the water pool in the micelles were different from those in the bulk state and were dependent on the w 0 value. In addition to such characteristics, since reverse AOT micelles have been utilized wide...

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Section: Energy Gap Dependence Of the Non-radiative Rate Constant Of Ansmentioning

confidence: 99%

mentioning

confidence: 99%

Energy Gap Dependence of the Nonradiative Decay Rate Constant of 1-Anilino-8-naphthalene Sulfonate in Reverse Micelles

et al. 1999

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“…It should also be noted that the maximum value of k obs for NBA is less sensitive to W o than in the reaction for PIP. Taking into consideration the higher polarity within the reversed micelles of AOT / n-hexane compare to pure n-hexane, 25 it can be assumed that these reactions do not undergo base catalysis in the micellar interface. Therefore, the experimental data could be explained by means of a mechanism that takes into account the distribution of the reactants between the micellar pseudophase and the bulk n-hexane, and the existence of two-reaction path, one in each phase, as it is summarized by the Scheme 1:…”

Section: Effects Of Aot Concentrationmentioning

confidence: 99%

Kinetics and mechanism for the reaction of 1-chloro-2,4-dinitrobenzene with n-butylamine and piperidine in AOT/n-hexane/water reverse micelles

Zingaretti¹,

Boscatto²,

Chiacchiera³

et al. 2003

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The kinetic profile of the S N Ar reaction of 1-chloro-2,4-dinitrobenzene with n-butylamine and piperidine in AOT/n-hexane/water reverse micelles were investigated as a function of variables such as AOT and amine concentration and the amount of water dispersed in the reverse micelles,The reactions in the micellar medium are faster than in the pure solvent. The pseudo-first order rate constants of the reactions go through a maximum when the AOT concentration is increased. Micellar interface saturation and no further micellar catalysis occurs at c.a. 0.1M of AOT. At higher AOT concentration dilution of the reactants in the micelles is the responsible of the rate decrease. In micellar medium a significant lost in the catalysis is observed compare with pure n-hexane. Thus, the reactions effectively take place at the interface of the aggregates. The kinetic behavior can be quantitatively explained taking into account the distribution of the substrate and the nucleophile between the bulk solvent and the micelle interface. A plausible mechanism to explain the results is proposed. Both the reactants distribution constants, between the micellar pseudo-phase and organic solvent, and the intrinsic second-order rate coefficients of S N Ar reactions in the interface were evaluated.

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“…[4][5][6][7][8][9] Among the surfactants capable of forming these aggregates, sodium 1,4-bis(2-ethylhexyl)sulfosuccinate (AOT, Scheme 1) is one of the most used. 10 Solutions of AOT in nonpolar solvents have the remarkable ability to solubilize a large amount of water with values of W 0 as large as 40 to 60, 11,12 depending on the surrounding nonpolar medium, the solute and the temperature.…”

Section: Introductionmentioning

confidence: 99%

“…The spectrum of the fully bound o-NA is red shifted by 24 nm regarding the initial spectrum of o-NA in n-heptane. Taking into account the studies in pure solvents 17 such a red shift can be partly interpreted owing to the greater polarity of the micelle interface with regard to the organic solvent 12 but also because the hydrogen bond acceptor ability of the polar heads of the surfactant. [17][18][19][20] Thus, in this system, o-NA is acting as hydrogen bond donor through the NH 2 group.…”

mentioning

confidence: 99%